This from Al Jazeera makes Turkey's aims a little clearer:
Major Yasser Abdul Rahim, who is also the commander of Failaq al-Sham, a main FSA rebel group in the operations room of the campaign, said the rebels did not seek to enter Afrin but encircle it and expel the YPG. "We have no interest in entering the city only the military targets inside the city and the villages around it. We aim to encircle the city and ensure the militias are evicted. We won't fight in the city as we have no problem with civilians," he said. A main goal of the military operation was to recapture Tel Rifaat, a town southeast of Afrin, and a string of Arab villages the YPG captured from rebels in February 2016, driving out tens of thousands of inhabitants, Abdul Rahim said.
Tension rises as Turkey sends troops to YPG stronghold | News | Al Jazeera